Chance of users have the cast function in the podcast app from Google two weeks ago received an extensive distribution but this was not yet. But they exist now. If the cast function is available in the app, you will see the corresponding cast button in the upper right corner. Thus, you can talk about the app also Chromecast Audio or Chromecast, podcasts thus more flexible on different devices.
For Smart Speaker itself, you do not need the Cast function, you can also directly command the speakers to play podcasts. Casting to other devices, the normal playback options are available, only the playback speed cannot be changed. The Cast functionality requires the Google app in version 8.22, which is currently being distributed by Google.